Paraffinic and asphaltenic hydrocarbons, as well as calcium carbonate and clays, may form undesirable deposits in boreholes and equipment used for the production of oil and gas from underground formations. The problem of removing such deposits is discussed in U.S. Pat. Nos. 5,152,907 and 6,242,388, and typically involves using an aqueous solution of an acid, such as hydrochloric acid, hydrofluoric acid, acetic acid, and the like, and mixtures thereof, in emulsified combination with a mutual solvent of oil and water.
Acidizing treatments are known to be corrosive, particularly in high temperature formations. In order to reduce corrosion, chemical additives have been used with acidizing treatment mixtures. Examples of typical chemical additives include corrosion inhibitors, intensifiers, acid retarders or emulsifiers, anti-sludge agents, friction-reducers, acid gelling agents, iron control or sequestering agents, mutual solvents, and surfactants. Use of these chemical additives is typically prohibitively expensive, as these additives may be required in high concentration in the acidizing mixture. In addition, a large amount of the corresponding acidizing mixture may be required in order to provide effective treatment. Finally, the effectiveness of traditional acidizing treatments has been limited to use at lower temperatures.
Mutual solvents have been used as chemical additives in acidizing treatments to prevent acid and crude oil emulsions, enhance water-wetting properties, and improve cleanup. In addition, mutual solvents have been used as a pre-flush or an after-flush alone or in combination with brine, acid or the like.